I drank the Kool Aid last week.
Crossed over into the third trimester and went in for the oh-so-pleasant glucose tolerance test to check for gestational diabetes.
As I choked down 75 grams of orange flavored liquid glucose, I thought to myself – “Who the hell came up with this pregnant woman torture test? You want me to fast and then drink something thick and sugary, continue to not eat or drink for two hours all the while pricking me like a pin cushion? Can’t you see that I’m pregnant? And, wait…why am I doing this again?” Really, how good is this one test at diagnosing and providing information for treatment?
To answer that first question – we can thank John B. O’Sullivan and Claire Mahan for developing the criteria to use with the oral glucose tolerance test in 1964 to screen for Gestational Diabetes Mellitus (GDM). And yes, forty years later, we still pretty much use the same test and the same criteria.
For the second question – digging through the scientific literature on this quest was a bit overwhelming and unsatisfying. Luckily, the National Institutes of Health recently put together a panel of experts for a Diagnosing Gestational Diabetes Mellitus Conference to tackle the scientific literature and give their expert opinion on the current status of diagnosing this disease in pregnant women.
From the statement issued, it seems that the discussion centered on whether or not to universally adopt a newer test pushed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG).
Two main tests are currently used across the world:
Two-step test – Pregnant woman drinks 50g glucose drink and has a single blood draw after an hour. If her glucose rides high, she has to go back and get the 3hr 100g test. This second test is strictly on an as-needed basis; only 14-23% of patients will need this diagnostic follow-up.
One-step test (promoted by IADPSG) – Pregnant woman goes in fasting, gets blood drawn, drinks 75g glucose drink, gets blood drawn at 1 hour and 2 hours. If any of her glucose levels ride high, for any of the three time points, she is diagnosed with GDM. This is the test that I was given.
For the two-step test, 5-6% of mamas-to-be will get diagnosed with GDM.
The one-step test is more prone to false positives. With only a one day, one time snapshot of sugar levels, this test does not exactly take into account the fact that results from the same woman can vary as much as 25% at different times. It is expected that this one-step test, with its current criteria, will diagnose 15-20% of pregnant women with GDM.
Considering this difference between the tests, the NIH panel statement focused on weighing the costs of underdiagnosing versus overdiagnosing GDM.
What are the risks of underdiagnosing?
First, what are the general risks of GDM? A study published in The New England Journal of Medicine entitled “Hyperglycemia and Averse Pregnancy Outcomes” by the HAPO Study Cooperative Research Group compiled data from over 25,000 pregnant women from 15 birth centers across 9 countries. All the women were given the one-step test and their glucose levels at any of the three sample points (fasting, 1 hr post glucose, 2 hrs post glucose) were correlated to primary risks (e.g. birth weight >90th percentile) and secondary risks (e.g. birth injury). They found that increasing relative glucose at any of the time points increases the likelihood of birth weight above the 90th percentile and the likelihood of c-peptide levels in the cord blood (a marker for insulin resistance in the baby) being above 90th percentile. There was also an increased risk of premature labor, preeclampsia, and birth injury.
Two things to consider though. One, these relationships are observational – correlations rather than causal effects. Therefore, outcomes cannot be clearly attributed to the increased glucose levels in the mother. Second, these increased risks and likelihoods have a linear relationship with glucose levels. There is no threshold so there is no easy cutoff point above when these levels cross into risky territory. Where do you draw the line for diagnosis?
Considering this diagnostic moving target, would all women at any range of GDM benefit from treatment?
Back to the NIH panel members, who pored over the literature for evidence and found…. well, there is really no consensus on the benefits of treating diagnosed GDM.
For the mother, treating GDM can decrease hypertensive disorders by 40% (one plus). For the baby, treatment decreases the likelihood of bigger babies (also a plus, BUT, at a 6% decrease, I’m not too impressed). Beyond these effects, there is no conclusive evidence that treatment decreases the other risks. Also important to note, these studies are based on treatment of women diagnosed by the more stringent two-step test. These are not women with mild GDM. We have no freaking clue how/if treatment will benefit those falling in the “hmmm…maybe” range.
What are the risks of over-diagnosing?
For one, being told that you’re pregnancy isn’t going as swimmingly as you thought and that you have to be on high alert, pricking your finger all the time to test your blood sugar could certainly cause a bit of anxiety.
Additional concerns discussed by the NIH panel:
One, this diagnosis has been linked to higher induction rates. Two, having “Gestational Diabetes Mellitus” on your chart could send you down a C section spiral – increased fetal and maternal monitoring which can then lead to increased false alarms which can lead to increased failed induction which can lead to increased cesarean section. Three, it can result in increased neonatal care, separating mama from baby unnecessarily. And, four, with all the heightened intervention, it can lead to increased direct and indirect health care costs.
Overall, the NIH panel warns that “overdiagnosis of GDM may lead to the ‘medicalization of pregnancy’ which transforms an otherwise normal pregnancy into a disease”
As the panel concluded, it is too early to universally adopt the one-step approach. Increased diagnosis will lead to increased cost and intervention without a clear cut benefit to the patient.
Basically, the answer to my second question is – the jury is still out.
I’m not sure how much say a woman can have in the type of test she is administered. If I had known all of this before, I might have asked if the two-step test was an option. Luckily my levels were totally normal. But I guess I could have just been caught on a good day at a good time…. Phew!
Overall, I agree with the NIH panel, why risk unnecessarily stressing out a pregnant woman? We have the rest of our lives to stress about all the ways we will screw up our kid!